WALTHAM 
Celtics rookie Jared Sullinger's strong preseason game performances in Turkey and Italy probably had some NBA general managers second-guessing themselves for not drafting him.

Sullinger gets no satisfaction from that.

“I could care less about them GMs at this point,” Sullinger said yesterday after practice at HealthPoint. “There's only one GM I worry about and that's the man upstairs (Danny Ainge). He gave me an opportunity to play here so I'm going to live it to the fullest.”

The former Ohio State star's stock dropped when back problems were discovered at the pre-draft camp in Chicago, so he was available when the Celtics made the 21st pick.

Celtics coach Doc Rivers has been a fan ever since Sullinger played AAU ball against his son, Austin.

“They trapped him every single possession,” Rivers said, “so he's seen every coverage that you could ever see. He's had to think his way through it. I think that serves him well.”

Rivers was on hand at the NBA draft when New Orleans drafted Austin 10th. Austin couldn't believe Sullinger fell into the Celtics' laps.

“He was like, 'This is unbelievable,' ” Boston's coach recalled. “He was shocked by that. He just kept saying, 'This is unbelievable.' ”

Rivers is grateful that news of Sullinger's bad back scared off other teams.

“If I could go back and redo everything,” he said on media day, “and me not getting hurt, I'd get hurt again and slide all the way back down to 21 just so I could be with the Boston Celtics.”

So far, Sullinger's back hasn't been an issue, but that doesn't mean it won't become one.

“He has to watch it,” Rivers said. “He has back issues like half the league. So he just has to take care of himself.”

The 6-foot-9, 260-pound forward contributed game highs of 16 points and 8 rebounds in 26-1/2 minutes off the bench in the preseason opener in Turkey. He started last Sunday in Italy and had 9 points and 7 rebounds in 18 minutes.

Sullinger, 20, played well against European power forwards who were known more for shooting than rebounding. Tonight, he'll get his first chance to prove he can hold his own against more physical big men when the Celtics play the New York Knicks in a preseason game at 7:30 at the XL Center in Hartford.

Sullinger was a consensus top-five player in the high school senior class of 2010, averaging 24.5 points and 11.7 rebounds for the nation's No. 1-ranked team, Northland High in Columbus, Ohio. Then he stayed in his hometown to play for Ohio State and averaged 17.5 points and 9.3 rebounds as a sophomore last year while leading the Buckeyes to the NCAA Final Four. OSU got there by winning the East Regional at the TD Garden. So he'll enter his rookie season with fond memories of his new home court.

“It's a blessing,” he said. “It's just God's way of telling me this was a special place to you and just letting me know that this is an organization I really want to be a part of.”

Fab Melo and Kris Joseph, Celtics rookies out of Syracuse, don't have such great memories of the Garden. Their college careers ended there when Ohio State beat the Orange in the East Regional final.

Sullinger said he's not determined to prove his doubters wrong by piling up big numbers, but Rivers wouldn't mind if he did.

“Six months into the college season,” Rivers said, “he was a top-three pick and then he goes 21. I wouldn't be very happy with that. But listen, he has to do it for 15 years to prove them wrong, not just one year. That's the way he has to look at it.”

Sullinger learned quickly how intense Kevin Garnett can be. Garnett has been in Sullinger's ear for much of camp.

“Everybody thinks it's in a bad way,” Sullinger said. “A lot of his talking is really in a good way. It's just the intensity, the way he nods his head, the way he moves his body, his body language. Everybody thinks that's negative, but really, half his stuff is positive.”

KG sometimes calls Sullinger “Sully,” the nickname Sullinger's mother uses, his two brothers and even his father. But KG calls Sullinger “young'un” most of the time.

“I'm his young'un,” Sullinger said. “I accept that being that he is an NBA dinosaur. You've got to understand that being young is a good thing.”